1. Field of the Invention
This invention relates to optic polymers and, in particular, to optical polymers prepared by reacting a polyene monomer, a polyisocyanate or polyisothiocyanate monomer and a monomer having at least two active hydrogen groups, and to a process for preparing such polymers and to optic products made from such polymers.
2. Description of Related Art
Polymeric materials are used extensively as substitutes for glass in optical products such as lenses. The use of polymeric materials over glass offers several practical advantages. Since polymeric materials have a lower density than inorganic glass, there can be a great reduction in weight of the optical product.
Additionally polymeric materials may offer great improvement over glass in terms of impact resistance. The improved processability and other characteristics such as tintability make polymeric materials especially attractive as a material for ophthalmic lenses. A variety of polymeric materials including polycarbonates, polystyrenes, acrylic polymers, polythiourethane, and polysulfones have already been used for optical applications. Each of these materials offers a somewhat different combination of physical and optical properties which lead to advantages and disadvantages for optical applications. For example, polycarbonate lenses typically show excellent impact resistance but are also characterized by poor scratch resistance and tintability and high chromatic aberration. Acrylic polymers have excellent optical clarity, but poor impact resistance and a relatively low refractive index. Polystyrenes are typically characterized by a relatively high refractive index, but also show a great deal of optical dispersion combined with poor impact resistance. Polysulfones have a high refractive index, but are typically colored and typically difficult to process.
Considerable research has been directed towards development of polymers with a combination of properties which make them well suited for optical applications. Generally, a high refractive index is of principal importance for an optical material since the use of a high refractive index material allows for production of thinner lenses when designing lenses of the same power and design. Reduction of edge thickness of the lens offers practical advantages in terms of weight savings and aesthetic reasons. Another important consideration for optical materials is optical dispersiveness. The value of optical dispersiveness is typically characterized by the Abbe""s number. Materials with high Abbe numbers show little optical dispersiveness while materials with low Abbe numbers show high optical dispersiveness. A high Abbe number is desired for optical materials since this will lead to reduced chromatic aberration and better image clarity for a given lens design and thickness. Typically polymers with high refractive indices also possess low Abbe numbers. An Abbe number close to 40 is 20 considered to be high enough for desired eyeglass application. The two most common plastic lenses in the market, polycarbonate and CR-39 lenses, have shortcomings in optical properties. Polycarbonate lenses, for instance, have a relatively high refractive index of 1.59 and a relatively low Abbe number of 30.4. Lenses made of diethylene glycol bis(allyl carbonate)(CR-39 resin) have a low refractive index of 1.49 and an Abbe number of 58. Therefore, when using an optical material, it is very important to balance refractive index and Abbe number so that both are suitable for the end product. Optimally, both refractive index and Abbe number should be high.
Several other considerations are of importance for optical materials, especially for use in ophthalmic lenses. Tintability and impact resistance have both become especially important properties for ophthalmic lens materials. Polycarbonate lenses are known for their excellent impact resistance; however, polycarbonate is extremely difficult to tint. Polythiourethane lenses may also possess good impact resistance, but elevated temperatures are required for tinting which may lead to possible lens deformation. Therefore polymers having improved tintability properties over these optical polymers is desired.
Weathering stability is another problem for most plastic lenses, especially for polythiourethane based lenses. Free xe2x80x94SH groups at the end of the polythiourethane polymeric molecules are readily oxidized by oxygen over a period of time or at elevated temperature and the lenses will become yellow. It is also the intention of the invention to reduce or eliminate free SH groups to enhance the weathering stability. Additionally, properties such as optical clarity and transmittance, coloration, hardness, machinability, processability and the like must also meet certain property levels in optical materials useful for use in optical products.
A number of patents have been granted directed to optical resins.
U.S. Pat. No. 4,689,387 is directed to a S-alkyl thiocarbamate base lens resin obtained by reacting one or more xe2x80x94NCO containing compounds with one or more xe2x80x94SH containing aliphatic compounds. The patent discloses using a radical-polymerizable raw material in the reaction in small amounts depending what requirements would be imposed as a lens resin, so long as these additional components do not prevent the attainment of the object of the subject invention. Radical-polymerizable raw materials such as diethylene glycol bis (allyl carbonate) (DAC), an acrylic ester, a methacrylic ester or a styrene derivative along with its radical polymerization initiator may be used in small amounts in the reaction mixture.
U.S. Pat. No. 4,775,733 claims a high-refractivity plastic lens resin consisting essentially of a polymeric reaction product obtained by copolymerizing a polyisocyanate with a polythiol.
U.S. Pat. No. 4,780,522 claims an optical lens comprising a copolymer obtained by reacting an isocyanate with an xe2x80x94OH containing compound having two or more xe2x80x94OH groups.
U.S. Pat. No. 4,946,923 claims an S-alkyl thiocarbonate base resin 5 comprising reacting a polyisocyanate with at least one hydroxyl-containing mercapto compound.
U.S. Pat. No. 5,084,545 claims a plastic lens comprising the reaction product of one or more isothiocyanate compounds with one or more polyol, polythiol, or polythiol-hydroxy compounds.
U.S. Pat. No. 5,310,847 claims a polyurethane composition suitable for optical lenses which is made by reacting a polyisocyanate free of intermolecular sulfur atoms and an acylic saturated monomer having at least three reactive groups with respect to isocyanates per molecule. The reactive groups may be mercapto.
U.S. Pat. No. 5,047,576 is directed to a polymerizable vinyl compound having a polythioether skeleton, which is prepared by addition-reaction of a polyene compound which is a specifically defined acryloyl or acryloyl amide having an aliphatic or alicyclic residue with at least one (1) polythiol compound in the presence of a basic catalyst.
U.S. Pat. No. 5,270,439 is directed to a method of producing a curable composition containing: 1.) a prepolymer having a polythioether skeleton made by addition reacting 4,4xe2x80x2-bis(methacryloythio) diphenylsulfide and a polythiol having the formula Rxe2x80x94(SH)m and 2.) at least one other vinyl monomer being copolymerizeable with the 4,4xe2x80x2compound in the presence of a base catalyst.
U.S. Pat. No. 5,352,757 claims sulfur compounds of the general formula [HSxe2x80x94R1xe2x80x94COO]xe2x80x94nA where R1 is a linear or branched alkylene radical containing one to three carbon atoms and A denotes a hydrocarbon residue of valency n chosen from four particular aromatic and cycloaliphatic radicals. The sulfur compounds are used in the preparation of polythiourethanes by reaction of the sulfur compound and an aromatic polyisocyanate. The sulfur compounds are also employed for preparing polythioethers by reaction with a polyene monomer. Both the polyurethanes and polythioethers obtained from the subject sulfur compounds have properties which enable them to be employed in optics. It is also disclosed that the polythiourethane and polythioether polymers formed may be used alone or mixed for optical purposes such as the manufacture of ophthalmic lenses.
U.S. Pat. No. 4,120,721 is related to a liquid radiation curable composition useful for coating and imaging which comprises: 1.) an acrylic or methacrylic terminated, urethane containing polyene, 2.) a non-water soluble vinyl monomer diluent, preferably an acrylate or methacrylate monomer diluent, 3.) a polythiol containing at least two thiol groups per molecule and 4.) a photoinitiator. The composition on exposure to radiation, e.g., a UV light source, cures to a solid polythioether.
Bearing in mind the problems and deficiencies of the prior art, it is accordingly an object of the present invention to provide polymerizable monomeric compositions and polymeric materials having a combination of properties which are superior in many aspects to that of existing optical materials. It is another object of the present invention to provide a process for preparing optical resins having a superior combination of physical and optical properties. The terpolymer system described herein offers advantages over poythiourethane homopolymers in that the terpolymers have reduced yellowness, enhanced tintability and weathering stability, as well as a reduced odor in the uncured resin. The terpolymer system offers advantages over polythioether homopolymer systems in terms of enhanced impact resistance and an enhanced refractive index and Abbe number combination.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
In this invention, it has been discovered that reacting effective amounts of polythiols with both polyenes, preferably with three (3) or higher number of vinyl groups in the monomers, and polyisocyanates results in a new class of terpolymers which are homogeneous systems without any significant phase separation and have enhanced properties for optical applications such as eyeglasses. Among these properties are a balanced high refractive index and high Abbe number, enhanced tintability and enhanced weathering stability and good impact resistance. The subject of this invention are optical resins having a combination of high refractive index and high Abbe number produced from curable or thermoplastic monomer compositions. The monomer composition is comprised of a polyene monomer, a polyisocyanate or polyisothiocyanate monomer or a polyisocyanate monomer containing at least one isothiocyanate group and a monomer having two or more active hydrogen groups such as hydroxy, thiol, NH, NH2 or mixtures thereof. By polyene monomer is meant a compound containing two or more vinyl groups. For convenience, the term polyisocyanate will be meant to include polyisocyanate, polyisothiocyanate, and polyisocyanate monomers containing at least one isothiocyanate group, or mixtures thereof.
A preferred polymer is formed by the reaction of a polyacrylate or polymethacrylate monomer, a polyisocyanate monomer and a polythiol monomer. Preferred monomers because of their demonstrated utility are pentaerythritol tetraacrylate, m-xylylene diisocyanate, pentaerythritol tetrakis(2-mercaptoacetate), pentaerythritol tetrakis (3-mercaptopropionate), 2-mercaptoethyl sulfide and 1,2-ethanedithiol. Another polyene which is preferred is triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-5trione.
In another aspect of the invention, a process is provided for preparing optical resin products with enhanced optical and physical properties from the composition comprising a polyene monomer, polyisocyanate monomer and active hydrogen groups containing monomer. Broadly stated, the process comprises preparing a mixture of the polyene monomer and polyisocyanate monomer under non-reactive conditions and cooling the mixture to a temperature, for example, less than about 15xc2x0 C. Adding the hydrogen group containing monomer, or mixture of such monomers, which are separately mixed under non-reactive conditions and cooled to a temperature, for example, below about 15xc2x0 C., to the polyene-polyisocyanate mixture and maintaining the temperature below reaction conditions, e.g., below abut 15xc2x0 C. An initiator is added for initiating the reaction and the mixture preferably degassed. The mixture is kept cool, e.g., at a temperature below about 15xc2x0 C. for up to 72 hours, preferably 10 to 32 hours and is then cast (cured) at an elevated temperature to produce the optical resin of the invention. A preferred curing process is also disclosed.
In another aspect of the invention, the optical resin products may be prepared by casting or other mold type polymerization process to produce a cross-linked resin optical product. The resin can also be formed as a linear thermoplastic polymer which polymer can then be injection molded or compression molded into optical and other products at high production rates.
As distinct from the prior art aforementioned, this invention does not use a small amount of radical polymerizable raw materials as additives in polythiourethane homopolymer systems, especially monomers with only one vinyl group such as styrenes, acrylic esters, methacrylic esters, because incorporation of these monomers in thiourethane systems will severely deteriorate mechanical, as well as optical properties of the resultant material which is not suitable for lens application with commercial value.